Articles in a wet environment, such as for example sweating pipelines, submerged oil lines or pipes, gas lines or pipes, and risers of drilling and production rigs or platforms are subject to corrosion or deterioration above, at and below the water line. These articles may be subject to deterioration or damage by salt water, corrosive pollution, cycles of wetting and drying, cycles of freezing and thawing and electrolysis. Erosion, marine organisms, mechanical impact, water content and abrasion may also cause premature failures of even properly designed articles. It is therefore necessary to protect such articles against damage or deterioration.
Corrosion is not only a problem with metal articles in a wet environment, but for example concrete articles may also be damaged by corrosion. Concrete may absorb water from the wet environment, resulting in corrosion of the (metal) reinforcement that is present in the concrete.
The anticorrosion treatments which have been carried out hitherto use quasi-manual techniques. The most widely practiced solution in fact consists in utilizing the services of divers, who, under several meters or tens of meters of water, manually coat the elements to be treated with, for example, paints, resins or mastics. Such techniques, practiced under difficult conditions, are very expensive, hazardous, and often rather unsatisfactory in terms of their effectiveness.
In addition to the adverse effects due to corrosion, submerged articles suffer the consequences of various mechanical stresses such as, for example, gravity, the repeated impact of the waves, the pressure of underwater currents or the traction on anchorage points. Offshore drilling and production platforms, in particular the risers, are relatively sensitive structures in this respect, by virtue of both their construction and their exposure to the natural elements.
In the prior art methods for anti-corrosion protection of structures in a marine environment and/or partly or wholly submerged structures are known wherein an encasing is used in combination with a corrosion inhibiting substance such as a curable polymer composition. Reference is for example made to U.S. Pat. No. 4,892,410, U.S. Pat. No. 5,049,005, U.S. Pat. No. 5,226,751 and U.S. Pat. No. 5,591,265, all incorporated by reference herein.
U.S. Pat. No. 4,892,410 discloses a jacket construction wherein a curable two-component polymer composition is injected and after which the polymer composition is cured. The polymer composition may for example be an epoxy resin.
U.S. Pat. No. 5,049,005 discloses a device for protecting branch girder joints against corrosion, said device comprising an elastic polymerized material such as for example an epoxy resin or a polyurethane.
U.S. Pat. No. 5,226,751 discloses a process wherein a jacket is placed around a pile which is then injected with air and preheated gas to dry the pile. In a subsequent step, the jacket is filled with an expanding closed cell form formed from liquid chemicals or epoxy resins.
U.S. Pat. No. 5,591,265 discloses a formwork, preferably comprising a tubular elongated member, wherein a curable resin material is injected between the annular space that is present between the metal article to be protected and the wall of the formwork.
The disadvantage of methods such as disclosed in U.S. Pat. No. 4,892,410, U.S. Pat. No. 5,049,005, U.S. Pat. No. 5,226,751 and U.S. Pat. No. 5,591,265 is that cured, rigid polymer compositions are used which generally have poor adhesion properties to the surface of the metal article. Moreover, such cured, rigid polymer compositions provide a hard seal that may split or tear under the influence of mechanical stress, e.g. wave actions. Another disadvantage of these materials is that volatile solvents are required when such materials are applied, said solvents being known as unfriendly to the environment. Additionally, after application of these materials, the solvents evaporate thereby leading to the formation of a micro-porous seal which is at least permeable for corrosive substances such as salts, water and moisture. Cured, rigid polymers are also not easily removed from the metal article while easy removal is important when repairs, replacements or inspections have to be carried out.
A number of methods that can be used to protect a pipe against corrosion or other types of damage are known in the art.
EP 1644433, incorporated by reference, discloses an improved apolar, non-thermosetting, fluid polymer composition. However, although this improved composition may be used under humid conditions, no condensation of water may occur on the surface of the article to be protected while said composition is applied.
EP 751198, incorporated by reference, discloses an apolar, non-thermosetting, fluid polymer composition that can be used for protecting underground metal articles against corrosion wherein the metal articles are in contact with moisture. Polymers comprising polyisobutene and/or poly(oxydimethylsilylene) which have a viscosity of between 60000 and 1200000 cSt (60 to 1200 Pa·s) at 20° C. are advantageously used. The preparation may contain one or more fillers. The preparation may also contain one or more products which optionally have been obtained directly from petroleum, such as for example bituminous products and paraffin-like products, for example petroleum gel and wax. The apolar, non-thermosetting, fluid polymer composition may be used to protect risers of oil drilling platforms, steel components and pipelines that are submerged in seawater. However, during the application of the composition, it is necessary that the surface of the riser, steel component or pipeline is essentially dry in order to achieve sufficient adhesion of the composition to the surface.
EP 826817, incorporated by reference, discloses a band-like covering for the sealed covering of structures. The covering comprises a base and a kneadable material, such as a paste. The kneadable material may comprise a liquid polymer which is non-polar and does not cure, such as for example petroleum products such as tar-like, bituminous-like, vaseline-like and rubber-like materials. Preferably, polymers comprising polyisobutene and/or poly(oxydimethylsilylene) which have a viscosity between 60000 and 1200000 cSt (60 to 1200 Pa·s) at 20° C. are used. The product may comprise one or more fillers. The product may also comprise one or more products which are obtained directly or indirectly from petroleum, such as for example bituminous products, paraffin-like products, for example vaseline and wax. The covering may be used in the off-shore industry, but during application of the covering the surface of the structure should be essentially dry in order to achieve sufficient adhesion of the covering to the surface.
A composition known in the art for the corrosion protection of fully submerged articles is STOPAQ® Subsea Compound, marketed by Stopaq Oil & Gas Services B.V. STOPAQ® Subsea Compound, comprising a wax, petrolatum and bentonite, can be applied on the surface of an article while the article is submerged.
A disadvantage of the Subsea Compound is that the range of operation is insufficient for certain applications. The operating temperature of the Subsea Compound is in the range of about −20° C. to about 35° C., although under certain conditions a maximum operating temperature of about 45° C. may be achieved. At temperatures higher than about 45° C. the composition becomes more liquid and does not adhere to the surface of the article sufficiently and drips off the surface. In addition, at temperatures above about 45° C. a phase separation may occur, wherein the petrolatum starts to separate from the bulk of the product. Due to the relatively low maximum operating temperature, Subsea Compound is not suitable for the protection of articles that are not submerged, e.g. those parts of partly submerged articles that are situated above the water level, or sweating pipelines. As a consequence, two different corrosion protecting compositions need to be used for an article that is partly submerged: Subsea Compound for the protection of the submerged parts (i.e. the parts situated under the water level) and a different composition for the parts that are situated above the water level.
Several compositions comprising a polyisobutene, a filler and a plasticizer are known in the art as water stop compositions.
For example in U.S. Pat. No. 4,558,875, incorporated by reference, an aqueously-swelling water stop composition consisting of 10 to 40 wt. % of rubber with polyisobutylene as main ingredient, 10 to 20 wt. % of silicate, 10 to 60 wt. % of bentonite, said silicate and bentonite acting as fillers, and 10 to 40 wt. % of plasticizer is disclosed. The polyisobutylene preferably has a Staudinger molecular weight Ms of 70,000 to 130,000, corresponding to a viscosity average molecular weight Mv of about 840,000 to about 2,220,000 g mol−1 (the viscosity average molecular weight Mv can be calculated from the Staudinger molecular weight Ms via the relation Mv=0.0233(Ms)1.56, see for example the ExxonMobil product brochure “Vistanex PIB: Vistanex Polyisobutylene Properties & Applications”, 2003, incorporated by reference). Preferred polyisobutenes are Vistanex® L-80, Vistanex® L-100 and Vistanex® L-140, having a viscosity average molecular weight of about 750,000 to about 2,350,000 g mol−1. The plasticizer may for example be a mineral oil softener, a vegetable oil softener, a fat, an oil, a paraffinic derivative, etc. The water stop composition may be extruded into an elongated water stopper that can be inserted in for example a joint gap to stop water at the gap. U.S. Pat. No. 4,558,875 remains silent about corrosion prevention.
U.S. Pat. No. 5,663,230, incorporated by reference, discloses water stop compositions that exhibit a controlled swelling or volumetric expansion upon immersion in water. An exemplary water stop composition comprises about 10-30 wt. % elastomer blend, about 15-30 wt. % filler, about 20-40 wt. % plasticizer, and about 25-35 wt. % water swellable bentonite clay. The elastomer blend comprises 50-60 wt. % thermoplastic elastomers (TPE), 10-20 wt. % of a cross-linked butyl rubber and 20-40 wt. % of polyisobutene. Preferably, the elastomer blend, which is present in the water stop composition in about 10-30 wt. %, comprises about 30 wt. % polyisobutene. Polyisobutene homopolymers having a molecular weight of about 10,700-11,900 (Staudinger), corresponding to a viscosity average molecular weight Mv of about 44,000 to about 53,000 g mol−1, such as the Vistanex® LM polyisobutenes, are preferred. Examples of plasticizers include process oils such as for example petroleum aromatic naphthenic oils, naphthenic aromatic oils, naphthenic paraffinic oils and paraffinic oil. Water stop compositions comprising 6.10-6.24 wt. % polyisobutene are disclosed. U.S. Pat. No. 5,663,230 remains silent about corrosion prevention.
In the art there is a need for a material for the protection of articles against corrosion that can be applied in a wet environment, and that has a broad range of operating temperatures. There is also a need for a material that is easy to apply to the articles to be protected, and that can be applied while the article is in said wet environment. Preferably, the material can be applied in a wet environment without the need for extensive pre-treatment of the article to be protected.